High Temperature Superconducting Wire Research Articles

Temporal resistance variation of the second generation HTS tape during superconducting-to-normal state transition

BackgroundThe quench process in high-temperature superconducting (HTS) wires plays an important role in superconducting power devices, such as fault current limiters, magnets, cables, etc. The superconducting device should survive after the overheating due to quench.MethodsWe studied the evolution of the resistance of the YBCO tape wire during the quench process with 1 ms time resolution for various excitation voltages.FindingsThe resistive normal zone was found to be located in a domain of about 1-4 cm long. The normal state nucleation begins in 40-60 ms after voltage is applied across the HTS tape. In subsequent 200-300 ms other normal state regions appear. The normal domain heating continues in the following 5-10s that results in a factor of 2–3 increase of its resistance.ConclusionsFormation of the normal domain during the quench process follows the same stages for different excitation voltages. Characteristic domain sizes, lifetimes and temperatures are determined for all stages.

Electromagnetic design of 10 MW class superconducting wind turbine using 2G HTS wire

This paper introduces design processes of 10 MW class superconducting generator for wind Turbine. Superconducting generator can produce 5 times stronger magnetic field than permanent magnet at least, which enables large scale wind turbine to function as a lighter, smaller and more highly efficient system. These processes are targeted for higher efficiency and shorter high temperature superconductor (HTS) wires to fabricate 10 MW class superconducting generator. Three different approaches will be described in these design processes. First design process focuses on the number of rotor poles. Secondly, 270 and 360 A operating current of superconducting field coil can be adapted as a design parameter in this process. Lastly, 3 and 6 kV line to line voltage of stator coil will be used to design 10 MW class superconducting generator.

Analysis of mechanical characteristics of superconducting field coil for 17 MW class high temperature superconducting synchronous motor

Superconducting field coils using a high-temperature superconducting (HTS) wires with high current density generate high magnetic field of 2 to 5 [T] and electromagnetic force (Lorentz force) acting on the superconducting field coils also become a very strong from the point of view of a mechanical characteristics. Because mechanical stress caused by these powerful electromagnetic force is one of the factors which worsens the critical current performance and structural characteristics of HTS wire, the mechanical stress analysis should be performed when designing the superconducting field coils. In this paper, as part of structural design of superconducting field coils for 17 MW class superconducting ship propulsion motor, mechanical stress acting on the superconducting field coils was analyzed and structural safety was also determined by the coupling analysis system that is consists of commercial electromagnetic field analysis program and structural analysis program.

Numerical simulations of the alternating current loss in round high-temperature superconducting wire with a hole defect

This paper presents a finite element model to solve the electromagnetic behavior and the AC loss in round high-temperature superconducting wire with a hole defect both in external field condition and self-field condition. The hole defect is assumed to be infinitely long along the wire. The model is based on the H formulation and the highly nonlinear E−J characteristic. The simulation results for the round superconducting wire with a hole defect and the one without defect are compared. It is found that the existence of the hole defect causes small reduction for the magnetization AC loss and large enhancement for the transport AC loss. The influences of the position and shape of the hole on the AC loss are also investigated. We find that the AC loss in external field condition decreases when the hole defect moves towards the edge of the superconducting wire from its center. However, the feature is opposite in self-field condition. Meanwhile, the influence of the shape of the hole on the AC loss is not strong in both conditions.

Engineering nanocolumnar defect configurations for optimized vortex pinning in high temperature superconducting nanocomposite wires

We report microstructural design via control of BaZrO3 (BZO) defect density in high temperature superconducting (HTS) wires based on epitaxial YBa2Cu3O7-δ (YBCO) films to achieve the highest critical current density, Jc, at different fields, H. We find the occurrence of Jc(H) cross-over between the films with 1–4 vol% BZO, indicating that optimal BZO doping is strongly field-dependent. The matching fields, Bφ, estimated by the number density of BZO nanocolumns are matched to the field ranges for which 1–4 vol% BZO-doped films exhibit the highest Jc(H). With incorporation of BZO defects with the controlled density, we fabricate 4-μm-thick single layer, YBCO + BZO nanocomposite film having the critical current (Ic) of ~1000 A cm−1 at 77 K, self-field and the record minimum Ic, Ic(min), of 455 A cm−1 at 65 K and 3 T for all field angles. This Ic(min) is the largest value ever reported from HTS films fabricated on metallic templates.

Test result of striated HTS compact cables for low AC loss

Large AC loss from the second generation (2G) high temperature superconducting (HTS) wires has been one of the major bottlenecks in power applications with HTS materials. Moreover, the large power applications also require the large current capacity from the HTS wires, which makes them produce larger AC losses. In order to reduce the AC loss from the HTS conductors with large current capacity, an HTS compact cable with some striations on the superconducting layers has been proposed. In this paper, we prepared some sample HTS compact conductors with striations, and measured their magnetization loss from the external magnetic field. We also made some slits on the superconducting layer of the HTS wire by laser cutting to reduce the aspect ratio of the superconducting layers. It would make the low eddy current loss and magnetic decoupling. Finally, the magnetization losses of the sample HTS compact conductors were measured and analyzed.

A Novel Multi-Terminal Based Evaluation Method for an HTS DC Power Cable

High current capacity is one of the advantages of a superconducting power cable system. However, it creates difficulties when experimenting to analyze its characteristics. Short-length superconducting cables for a laboratory-scale experiment system present problems: large operating current and current distribution by terminal resistance. Experimental conditions, such as transient states, are limited by power supply capacity. In this paper, the authors suggest a new experimental method for the high-temperature superconducting (HTS) power cable to reduce the capacity of a power supply and solve current distribution problems. For the suggested method of this paper, each HTS wire has separated terminal and each HTS wire was connected in series through the separated terminal. All of HTS wires in the HTS power cable are insulated and connected in series. The cross-sectional area of the HTS power cable is the same, but the terminal structure is different. Thus, all HTS wires have the same current and cross-sectional area of HTS power cable. It is possible to test a large capacity HTS power cable under the transient state or fault conditions using a small-size power source. The design concept, configuration of the experiment system, and the experimental results were discussed in detail in this paper.

Design of a Test Bench for $\hbox{MgB}_{2}$ and HTS Wires

An innovative test bench for high-temperature superconducting (HTS) cables has been designed and is presently under construction at the Cryogenic Laboratory of the University of Ferrara and INFN-Ferrara, Italy. The aim of the test bench is to measure the critical current as a function of tension or compression of a straight MgB <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> and HTS wire at their working temperature. Currents up to 600 A will be supplied to a 120-mm-long wire, which can be cooled down to 20 K by cold-heads in vacuum. A piece of information from the traction bench will be synchronized with the power supply and quench protection system. Because the stress is constant on the wire cross-section, the measurement of the properties of a straight-wire represents a direct measurement of the strain behavior of the HTS wire. The full mechanical design will be illustrated together with the complete data acquisition system.

Effect of Length Scale on Critical Current Measurement in High Temperature Superconductor Wires

Measured variations in the local critical current (Ic) along the length of second-generation high-temperature superconductor wires depend surprisingly strongly on the voltage measurement gauge length. Longer gauge lengths can give the appearance of higher Ic uniformity than is actually present, and understanding this gauge length effect is essential for insuring that second-generation wires meet commercial specifications. The effect can be understood from the moderate index value n, which characterizes the voltage-current relationship (V ~ In) and is often found to be in the same range for regions of lower as well as higher critical current. In this paper, we present data demonstrating the gauge length dependence of the measured minimum local Ic and discuss a simple model based on earlier work of Friesen and Gurevich, which explains the effect and highlights the importance of measuring long length wires with short gauge lengths.

Study on Thermal Response to Instantaneous Heat Generation in LN2 Chamber for HTS-FCL

This paper describes the thermal response of a high-temperature superconducting (HTS) wire model to instantaneous heat generation in a pressurized liquid nitrogen chamber for an HTS fault current limiter. A dc impulse power input to a stainless steel strip is adopted to simulate the quench state of the HTS wire. The test sample is submerged in the liquid nitrogen, which maintains a 77 K temperature with operating pressures of 101, 250, 400, and 600 kPa. Three different levels of dc current are supplied to the test sample during 50 ms for each operating condition. The boiling phenomena are captured with a high-speed camera and the surface temperature of the sample strip is measured to investigate the recovery process. From the captured video, the suppression of bubble generation is clearly observed as increasing operating pressure, especially for the lower heat flux condition. From the measurement of temperature, temperature rise of sample strip during heat generation decreases with increasing operating pressure except for the higher heat flux. For the recovery process, increasing operating pressure delays the recovery of the sample strip, but recovery time is within a few seconds for all cases.

Helium-Neon Gas Mixture Thermosyphon Cooling and Stability for Large Scale HTS Synchronous Motors

Commercial high-temperature superconducting (HTS) wires restrain us to an operation temperature ranging from 20 to 40 K for field-pole magnets applied to rotating machinery. We have proposed to employ a mixture of helium and neon gas in a closed-cycle thermosyphon based on a GM cryo-refrigerator. In this paper, we discuss the temperature stability of the evaporator created by a helium-neon mixture cooling coupled with a closed-cycle thermosyphon, upon an external heat load on a 100-kW-grade HTS synchronous machine. A home-made cooling system, including the condenser, was designed. The evaporator was assembled within the motor in accordance with thermal and mechanical analysis. The cooling of the evaporator with the 100-kW-grade HTS synchronous motor was applied against a variable heat load equivalent with the actual HTS rotor field poles. We report these results and propose its potential application to a large-scale ship propulsion motor.

An Effect of HTS Wire Configuration on Quench Recovery Time in a Resistive SFCL

We experimentally investigated the correlation between the high-temperature superconducting (HTS) wires configuration in an HTS element and recovery time after quench in a resistive superconducting fault current limiter. The variables of the configuration are horizontal and vertical gap distances between HTS tapes in an element. Eight samples were made with different gap distances and tested. A SUS-stabilized YBCO tape with 4.4 mm width had been used in the experiment. It was cooled by LN2 in a cryostat under the pressure of 1 bar, saturated state. In the short-circuit test, the temperature of the wire's surface was measured. Recovery time of the HTS sample increased with decreasing horizontal and vertical gap distance due to stagnation of bubbles. When the gap distance was larger than a size of a bubble, the effect of gap distance was ignorable. Considering a volume and recovery time, the sample that has narrower gap distance was favorable.

Stator Winding Fault Influence on the Field Coil of a 10 MW Superconducting Synchronous Generator

It is important to analyze the transient characteristics of large synchronous generators according to the trend of the extension of wind turbines. The fabricated field coil of a synchronous generator using high-temperature superconducting (HTS) wire is somewhat influenced by the external magnetic field of the stator in a real environment. This paper describes the electromagnetic analysis of an HTS field coil of a 10-MW superconducting synchronous generator during stator winding faults. The real-time digital simulator is used to simulate a fault condition of the 10-MW SCSG. Also, the finite-element method is used in each operating condition, including normal and transient conditions, to analyze the influence of the HTS field coil. Based on the simulation results discussed here, there do not appear to be any significant problems regarding the electromagnetic operation of the HTS field coil during transient conditions of the stator. This paper will be used in the analysis of the transient characteristics of a large superconducting synchronous generator during stator winding faults.

Long-Length Coated Conductor Copper Plating Fabrication

Most application of high-temperature superconducting (HTS) wires require conductor engineering with respect to superior electric and mechanical properties and robustness. A long-length reel-to-reel Cu plating manufacturing technology was developed, tested, and transferred to the Bruker HTS production facility. Details of the design and the structure of the plating unit as well as plating results are reported. The pulse-plating technology provides a high quality of one- or two-sided metallic Cu layers on the surface of the pulsed laser deposition synthesized HTS tape. Acidic copper sulphate CuSO4 has been tested to optimize and enhance the plating process with respect to the Cu deposition rate. Using reel-to-reel mode together with the 6-m-long plating apparatus, up to a 2000 m length conductor has been treated with our unique Cu-plating technique, yielding reproducible Cu stabilizer performance with deposition speeds of up to 50 m/h. The plating technology is considered to have a high flexibility in processing a metallic copper stabilizer of a thickness of 5-50 μm. The resulting Cu-layered conductor has allowed face-to-face standard soldered joints of 10-7 Ωcm2 resistance to become routine. This work describes the overall analysis of the constructed reel-to-reel plating unit and evaluates the final conductor properties.

Design of a 400 mH 400 A Toroid-Type HTS DC Reactor Magnet

Large electric power systems, such as high voltage direct current (HVDC) transmission systems, need dc reactors with large inductance and high transport current. Such systems experience a lot of electrical loss due to the resistance of their copper winding. Employing superconducting magnets for the reactors provides some advantages such as high current density, low electrical loss, and so on. This paper describes the design of a toroid-type high temperature superconductor (HTS) dc reactor magnet. The target inductance and the current level of the HTS dc reactor were 400 mH and 400 A, respectively. The toroid-type HTS magnet reduced leakage flux and increased the critical current of the reactors. The HTS dc reactors were designed using 2G HTS wires. The Finite Element Method was used for the design and analysis of the toroid-type HTS dc reactors.

Cool-Down and Thermal Performance Test for Toroidal Configuration HTS SMES

The high-temperature superconducting (HTS) magnetic energy storage system working temperature is around 20 ~ 30 K because the HTS coils must be cooled below the critical temperature. In this paper, we have designed a system with an operating temperature of 15 K or below for the purpose of full utilization of the HTS wire material, minimization of the hardware dimension, and stable operation. For the cooling, four of 2-stage Gifford-McMahon coolers were used. The cooling system has a short and uniform thermal passage from the cryocooler head to each HTS coil for an effective cooling of HTS coils. The cold head first stage cools the thermal shield and current lead, and the second stage cools the HTS coils. Our full system has a total of 28 double pancake coils forming a toroidal configuration. For this study, we assembled a test set consisting of six dummy double pancake coils for cooling and load tests without charging current. This paper describes the cool-down and the thermal characteristics of the conduction cooling system. The modified cooling method is optimized for cool-down time reduction, and thermal tests were performed with heat loads up to 300 W.

Development and Performance Analysis of a 22.9 kV/50 MVA Tri-axial HTS Power Cable Core

Tri-axial high-temperature superconducting (HTS) power cables are being developed to maximize their advantages such as reduced amount of HTS wires, a low-leakage magnetic field, and compactness compared with the different types of HTS power cables. The authors designed a 22.9 kV/50 MVA-class tri-axial HTS power cable core to apply to the distribution system in Korea. The inherent imbalance in the three-phase currents of the tri-axial HTS power cable core was calculated using the impedance matching program. A tri-axial HTS power cable core was fabricated using second-generation YBCO wires and the cable core was tested under 77 K liquid nitrogen to verify the performance of the cable core through obtaining its electrical characteristics data. This paper describes the results of the design, fabrication, and evaluation of the 22.9 kV/50 MVA-class tri-axial HTS power cable core. They will be used to develop a tri-axial HTS power cable for the distribution system.

Testing Results for the Cable Core of a 360 m/10 kA HTS DC Power Cable Used in the Electrolytic Aluminum Industry

IEE has installed a 360-m-long high-temperature superconducting (HTS) dc power cable at the self-supply power plant of Zhongfu Industrial Co., Ltd. in Gongyi, Henan. The cable connects a 19.5 MVA/1.5 kA silicon-controlled rectifier, which connects with a 110 kV/1 kV transformer, to the bus bar of an electrolytic aluminum cell. It is designed to carry 10 kA current and the voltage is 1300 V. The HTS dc power cable core consists of five conductor layers wound with the spliced Bi-2223 wires with the length of 40 km. The cable core has five layers and 23 HTS wires in each layer with the outer diameter of 45 mm. As the items in this project, testing of 4 to 5 m length prototype cables, including a 5 m prototype cable fabricated before the 360 m power cable and a 4 m prototype cable intercepted from the 360 m HTS power cable, is conducted. These prototypes are used to assess the design program, fabrication process, and performance of the 360 m/10 kA HTS power cable including steady state operation at the 10 kA design current and overcurrent fault capability. The critical current of the 5 and 4 m HTS power cable reach 14.3 kA and 13.8 kA at 77 K, 1 μV/cm, respectively. In this paper, the design parameters and fabrication of the 360 m/10 kA HTS dc power cable conducted by IEE are presented. The cable system, installation process and the summary of the results from the testing of 4 and 5 m prototype cables are described. In addition, details of the initial cool-down process and energizing are presented.

Basic Study of IPMSM with High-Temperature Superconducting Wire Rod

It is important to improve the efficiencies of motors to overcome problems such as decreasing energy reserves and environmental pollution. Superconductors are promising for developing high-efficiency motors. However, superconducting wires must be kept in critical conditions and the AC loss needs to be minimized. In this paper, a design of a superconducting interior permanent magnet synchronous motor (IPMSM) is proposed that reduces the AC loss. The characteristics of superconducting and normal-conducting IPMSMs are compared. The proposed superconducting IPMSM has a low AC loss and a very high efficiency at low speeds.

Does the electric power grid need a room temperature superconductor?

Superconductivity can revolutionize electric power grids, for example with high power underground cables to open urban power bottlenecks and fault current limiters to solve growing fault currents problems. Technology based on high temperature superconductor (HTS) wire is beginning to meet these critical needs. Wire performance is continually improving. For example, American Superconductor has recently demonstrated long wires with up to 500A/cm-width at 77K, almost doubling its previous production performance. But refrigeration, even at 77K, is a complication, driving interest in discovering room temperature superconductors (RTS). Unfortunately, short coherence lengths and accelerated flux creep will make RTS applications unlikely. Existing HTS technology, in fact, offers a good compromise of relatively high operating temperature but not so high as to incur coherence-length and flux-creep limitations. So – no, power grids do not need RTS; existing HTS wire is proving to be what grids really need.